Field of the Invention
The present invention relates to an image forming apparatus such as copying apparatus, laser beam printer, or the like and, more particularly, to an image forming apparatus for controlling each section in the apparatus by using a fuzzy inference.
Related Background Art
Hitherto, in a control unit of an image forming apparatus, a formulary control is executed on the basis of a definitive judgment according to state amounts.
For instance, for a fixing device in the image forming apparatus, generally, a temperature of fixing device is detected by a heat sensitive element such as a thermistor or the like and a heat source such as a heater or the like is controlled on the basis of a predetermined temperature level as a threshold level. That is, when the detected temperature is lower than 180 .degree. C., the heater is made conductive (turned on), and when the detected temperature is higher than 180.degree. C., the conduction of the heater is stopped (turned off), or the like.
On the other hand, as an improvement method to reduce a fluctuation for a target temperature, various methods such that a heater ON-time is made variable in accordance with the present temperature and the like have been proposed.
However, in the image forming apparatus such as a copying apparatus or the like, generally, a fluctuation by circumstances is large and in many cases, the relation between the state amounts and the operation amounts is dominated by a vague relation. Therefore, in almost all of the cases, it is difficult to formulate the control as in the conventional example as the number of state amounts increases.
For example, in the temperature control of the fixing device, in the case where the state amounts such as room temperature, number of copy sheets, density of original, kind of recording medium (sheet type), temperature of fixing device itself, and the like fluctuate, the fixing capability to fix the toner which was copy transferred onto a copy transfer paper also complicatedly fluctuates. Such an experimental relation has been known. However, it is difficult to formulate the relations among the state amounts and the operation amounts. Practically speaking, degrees of heat radiation differ depending on the environment and the paper feeding/non-feeding states. When executing the control such as to turn off the fixing device when the temperature of fixing device itself is equal to or higher than a predetermined temperature and to turn on the fixing device when it is equal to or lower than the predetermined temperature as in the conventional apparatus, a temperature fluctuation (hereinafter, referred to as a temperature ripple) occurs, so that it is necessary to set the minimum value of the temperature ripple to a temperature enough to fix the toner to the copy transfer paper. Therefore, it is necessary to set a temperature adjustment set temperature to a value which is further slightly higher than an ideal temperature state. Consequently, there are problems such that a surplus electric power is consumed and it is necessary to use materials having a higher heat resistance as parts constructing the fixing device.
A technique to calculate operation amounts by executing a fuzzy inference to the vague relations among the state amounts and the operation amounts has been proposed by the same assignee as the assignee of the present invention in U.S. patent application Ser. No. 07/536,330 filed Jun. 7, 1990, now abandoned.
On the other hand, almost all of the control systems of the image forming apparatus execute what is called a feedback control such that an operation amount is determined to thereby control a control object and a degree of change of the operated amount of the control object by the operation amount is detected, thereby again deciding the operation amount. In such a feedback control system, it is unavoidable that a delay of the control system occurs in, particularly, the stabilization of the control response.
It is also considered that the delay of the control system is reflected into the fuzzy rules or membership functions in the fuzzy inference. However, even by using only such a method, it is difficult to sufficiently cope with a change in delay due to a variation in manufacturing of state amount detecting means or apparatus, an aging change, and the like.
The above problems are not limited to the fixing device. In an image forming apparatus of the electrophotographic type, such problems can also occur in, for instance, charging means, exposing means, copy transfer means, recording medium feeding means, conveying means, and the like.
The image forming apparatus is not always limited to the electrophotographic copying apparatus but the problem of the delay of the control system also similarly occurs in an ink jet printer, a thermal printer, and the like.